This invention relates to the field of chemically bonded molds. Particularly, the present invention relates to the release of precision cast parts from molds formed of high quality sand, a chemical binder and a catalyst which are hardened into a solid mold. When it is desired to remove the cast part from the mold, the mold shell can be removed as by blasting. This technique has the advantage that, in addition to removing the mold, the finish of the casting is improved. In order to use this technique, it is necessary to use high quality sand which may cost significantly more than coarse or green sand. Thus it is very desirable to reclaim the sand used in the molding process for reuse. The problem with reclaiming and reusing the sand is a buildup of fines and organic contaminants which increase the loss on ignition (LOI) of the sand and reduce its qualities as a high performance molding material.
Over a period of time the high quality sand breaks down through the repeated molding and blasting process into a fine dustlike material. This phenomenon is objectionable in that it adversely affects the mold strength and casting quality. Thus it is desirable to reduce the buildup of contaminants on the individual sand grains and to further maintain the initial screen size distribution of sand particles by removing particles which are of insufficient size.
In U.S. Pat. No. 3,716,947 to Carpenter et al. there is disclosed an abrasive cleaning system wherein sand molds are subjected to an abrasive blast for breaking the mold into small lumps. The lumps are then conveyed on a vibrating conveyor to a second blasting station where the lumps are broken down into individual discrete particles. By means of various elevators and screw conveyors, the material is conveyed to air wash separators for separating the sand from the particulate or abrasive shot. While such a device accomplishes its intended purpose, it does not provide means for maintaining a desired screen size distribution and further, it requires a plurality of blasting stations to break the sand down into discrete particles. Further, as indicated by U.S. Pat. No. 3,782,643, a continuation-in-part of the first-mentioned patent, there is an insufficient reduction in the contamination of the sand particles when the two-stage blasting technique is utilized. Thus, in order to compensate and further reduce the LOI problem, an additional technique for cleaning the sand is necessary, as disclosed in the second mentioned patent.